Electrostatic Spraying Microspheres of Nano Boron and Its Constant-Volume Combustion with Potassium Nitrate

The nanometer boron (nB) powders have become the most promising high-energy additive in the field of fuel-rich solid propellants due to their extremely high gravimetric and volumetric calorific value. However, further applications are limited by its disadvantages such as easy agglomeration, easy oxidation, high ignition temperature, and incomplete energy release. Herein, nB powders were pre-agglomerated into microspheres by electrostatic spray method using fluoropolymer (F2602) as binders. The morphology and structure of the samples were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray energy spectrometry (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), and Brunauer-Emmett-Teller (BET). Results showed that the pre-agglomerated nB microspheres had good dispersion, high sphericity, and no surface oxide. The thermal performance and combustion performance of the samples were characterized by a synchronous thermal analyzer and combustion pressure test device. Results showed that the nB microspheres had the highest oxidation weight gain within 1000 degrees C and lowest activation energy compared to the same scale micron boron. In addition, the microspheres significantly shorten the combustion time and improve the combustion efficiency.The pressurization rate of nB microspheres is 4.12 times that of micron boron powders and 2.85 times that of nB powders. These excellent properties may be related to its unique spherical porous structure. Therefore, the preparation of nB microspheres with controllable structure by electrostatic spraying has a good application prospect.